1. Field of the Invention
The present invention relates generally to a recording system and, in particular, to a recording system for accumulating image data in a memory and then recording the image data in a recording medium.
2. Description of the Related Art
Digital video disc (DVD) cameras are known in which captured image data are recorded in a DVD in a digital data format. In order to protect against shock and to reduce power consumption at recoding time, Japanese Patent Laid-Open No. 6-52636 discloses a recording system in which captured moving image data is buffered in a built-in image memory and the buffered image data is recorded into a disk after a predetermined amount of image data is accumulated in the image memory.
In general, image data for a duration of several seconds to several tens of seconds is buffered. The duration for the buffered image data varies depending on the capacity of the built-in memory and recording speed (rate) of the recording medium.
For example, if image data of 10 seconds is recorded into a disk after being stored in a memory, image data for 300 frames is buffered in the NTSC standard.
Additionally, when image data is recorded in a disk medium and is played back from the disk medium, the pickup head which reads and writes the image data is precisely controlled in order to align the position (tracking). For example, if the head position is offset due to an impact force on the system, a re-tracking of the head is needed. This may cause recording failure or play back failure if the re-tracking occurs many times.
Consequently, to ensure the stability of recoding and playing back, a predetermined amount of image data is buffered in the built-in memory and the buffered data is recorded in a disk in a short time when recording, while a predetermined amount of bulk image data is played back from the disk in a short time, is buffered in the built-in memory, is read out, and is output when playing back.
Among such video cameras, some have an interval recording function that captures image data for a predetermined duration at predetermined intervals as well as normal recording functions.
More specifically, the interval recording function repeatedly captures image data for a predetermined duration, for example, a duration of several frames, at predetermined intervals, for example, intervals of several minutes. Some video cameras allow a user to freely set up a shot-to-shot interval, a recording time for one shot, and also a duration in which a re-recording is executed (i.e. the number of repetitions).
The interval recording is suitable for recording changes in a subject that take a long time by using a video camera that is mounted on a tripod and in which the field angle remains constant. For example, it is suitable for shooting changes when a flower is opening up.
However, when, as described above, a predetermined amount of image data is recorded in a disk after being buffered in a memory, the following problem occurs in the interval recording.
Assuming that 2 frames are captured at one shot and 300 frames of image data can be stored in a memory, image data for 150 shots can be buffered.That is, 300 frames/2 frames=150.
Accordingly, if a recording interval is 1 minute, the image data stored in the buffer memory is recorded in a disk at intervals of 150 minutes.
During interval recording, the total shooting time frequently becomes long since a change in a subject for a long time must be shot at predetermined intervals. For example, the opening of a flower sometimes requires several tens of hours.
Since the shooting requires a long period of time, it is difficult for a user to monitor the state of the system at all times. And when the camera uses a battery, the camera may stop functioning due to a drop in driving voltage supplied to the system. If the recording is carried out using an AC power supply, the recording may also stop due to power blackout.
In these cases, the driving power supply that operates the system is lost. Therefore, not only is the image data stored in the memory not recorded in the disk, the buffered image data is cleared.
For example, in the above-described conditions, the image data captured by the interval recording during a maximum of 150 minutes, that is, the 10-second image data to be recorded is discarded without being recorded in the disk.
Thus, in the interval recording, when the recording system becomes inoperable due to, for example, power blackout or shut-off of power supply to the recording system, image data captured before the shut-off may not be recorded.